This invention deals generally with fire escapes, ladders and scaffolds, and more generally with a rotating coupling used at the base of an aerial ladder to transfer fluids and electrical circuits to the ladder.
Aerial ladder trucks for fire fighting are no longer the simple extension ladders on trailers which are seen in old movies or as children's toys, and up which firemen once pulled conventional fire hoses. A modern aerial ladder truck has hydraulically operated ladder lifting and rotating motors, a vast number of electrical accessories permanently installed atop the ladder, and a permanent high pressure water supply pipe which is built right into the ladder tower. Furthermore, these modern aerial ladder trucks include controls located atop the ladder, so that a fireman stationed there can fully control the ladder and also control all the electrical functions available.
Such devices therefore require passing high pressure water, several hydraulic control lines, and multiple electrical connections through the rotating joint between the ladder and the support truck, and since the major focus of the rotating joint has been to transfer a large quantity of high pressure water across the rotating joint, the configuration of such rotating couplings has been largely determined by the size of the water coupling. Such couplings therefore usually are constructed with a large central pipe rotating relative to a surrounding body, with the pipe and body sealed against water leakage by the use of conventional "O" ring seals mounted within annular channels within one of the parts.
The auxiliary functions, such as the rotating hydraulic fluid couplings and the rotating electrical connectors, are then built around the large central water coupling, and extend out along the length of the axis of the water coupling. Typically, each hydraulic line rotating coupling requires an annular channel to contain hydraulic fluid and additional channels with two "O" ring seals and their associated annular channels on either side of the hydraulic channel. Since it is typical to include at least four such sets for the transfer of hydraulic lines across the rotating joint, a considerable distance along the length of the rotating coupling is used up by the hydraulic line couplings.
The transfer of electrical lines across the rotating joint also uses more of the length along the axis of the rotating coupling. Existing rotating couplings use sets of mating conductive slip rings and contacts for each wire crossing through the rotating coupling. One part of each set is attached to the rotating pipe section of the coupling and the other part is attached to the stationary body assembly. Since modern aerial ladder trucks require many electrical circuits for lighting, control, and communication, and each circuit requires several wires crossing the rotating joint, many slips rings must be stacked axially along the joint. This usually requires either that the assembly be made longer than would otherwise be required, or that the number of electrical circuits be limited.
The present invention furnishes a novel configuration for the electrical connections of a rotating coupling for an aerial ladder truck. This configuration reduces the distance along the axial length of the water coupling occupied by the rotating electrical couplings, and therefore permits many more circuits to be included within a rotating coupling without increasing its size.